1. Field of the Invention
The present invention relates to a method and related controller capable of sensing a heavy load and a short circuit of a low dropout regulator, and more particularly, to a method and related controller that compares a feedback signal of the low dropout regulator with a square waveform to determine a heavy load and a short circuit.
2. Description of the Prior Art
Generally speaking, supply voltages utilized by integrated circuit chips come from systems. For examples, supply voltages for network chips, wireless communication chips, or image processing chips disposed in desktops or laptop computers are provided by motherboards. However in a general case, input voltages (such as 5V or 3V) generated by systems are too high to be used directly as supply voltages (such as 1.5V) in IC chips unless certain voltage converting circuits first convert input voltages into a lower voltage level that suits IC's use.
Typical voltage converting circuits include switching regulators and linear regulators. Switching regulators achieve high power efficiency. For example, if a 3V input voltage is to be converted into a 1.5V supply voltage, the switching regulator achieves high power efficiency, even close to 90%, but an off-chip inductor or capacitor is required. Off-chip components such as inductors or capacitors are not only expensive but also large in volume. Besides, the switching regulator causes ripple effects at the voltage output, and results in unstable output voltages. Linear regulators have strong points of quick response, stable output voltage, and low noise and always are applied to analog circuits or critical voltages. A common linear regulator such as a low dropout regulator is applied to stepdown only due to the low dropout regulator having high power consumption and low transformation efficiency although it has strong points of low cost, small package, and low noise. The transformation efficiency of a low dropout regular having a 3.6V input voltage and a 1.5V output voltage is merely 41.7% due to the transformation efficiency of the low dropout regular depending on ratio of the output voltage to the input voltage. Such low transformation efficiency not only wastes energy but also causes chips to have a temperature that may influence system stability when output currents are large.
Please refer to FIG. 1 that is a diagram of a low dropout regulated circuit 10 in the prior art. The low dropout regulated circuit 10 includes a low dropout regulator 12 and a controller 14. The low dropout regulator 12 is used for transforming an input voltage Vin into an output voltage Vout where the output voltage Vout is smaller than the input voltage Vin. The controller 14 is used for driving the low dropout regulator 12 and includes a driving transistor Q1, a first resistor R1, a second resistor R2, a capacitor C1, and an output capacitor Cout. The driving transistor Q1 has a control end 102, a first end 104, and a second end 106. The control end 102 is used for receiving a driving signal DRV1, the first end 104 is used for inputting the input voltage Vin, and the second end 106 is used for outputting the output voltage Vout. The capacitor C1 is coupled between the input voltage Vin and the first end 104 of the driving transistor Q1 for filtering noise of the input voltage Vin.
The first resistor R1 has a first end 312 and a second end 314. The first end 312 is coupled to the second end 106 of the driving transistor Q1, and the second end 314 is used for outputting a feedback signal FB1. The second resistor R2 has a first end 322 and a second end 324. The first end 322 is coupled to the second end 314 of the first resistor R1 in series, and the second end 324 is coupled to ground. A magnitude of the feedback signal FB1 is decided by a ratio of the first resistor R1 to the second resistor R2. The output capacitor Cout is coupled to the output voltage Vout as a loading of the low dropout regulator 12.
The controller 14 includes an amplifier 15. The amplifier 15 has a first input end 152, a second input end 154, and an output end 156. The first input end 152 is used for receiving a reference voltage Vref, the second input end 154 is coupled to the second end 314 of the first resistor R1 and to the second end 324 of the second resistor R2 for receiving the feedback signal FB1, and the output end 256 is coupled to the control end 102 of the driving transistor Q1 for outputting the driving signal DRV1 to the driving transistor Q1. The amplifier 15 outputs the driving signal DRV1 in high level to the driving transistor Q1 and the driving transistor Q1 is turned on when the reference voltage Vref is greater than the feedback signal FB1. The low dropout regulator 12 transforms the input voltage Vin into the output voltage Vout normally. The amplifier 15 outputs the driving signal DRV1 in low level to the driving transistor Q1 and the driving transistor Q1 is turned off when the reference voltage Vref is smaller than the feedback signal FB1. The driving transistor Q1 is a metal-oxide semiconductor transistor (MOS).
Please refer to FIG. 2 that is a diagram of a low dropout regulated circuit 20 in the prior art. The regulated circuit 20 includes a low dropout regulator 22 and a controller 24. A difference between FIG. 1 and FIG. 2 is that the driving transistor Q1 is installed inside the controller 24 of the low dropout regulated circuit 20 and a current I1 flowing into the driving transistor Q1 is calculated by a resistor R. The low dropout regulator 22 is used for transforming the input voltage Vin into the output voltage Vout where the output voltage Vout is smaller than the input voltage Vin. The controller 24 is used for driving the low dropout regulator 22.
The low dropout regulator 22 includes the first resistor R1, the second resistor R2, the capacitor C1, and the output capacitor Cout. The controller 24 includes an amplifier 25, the driving transistor Q1, and the transistor R. The driving transistor Q1 has the control end 102, the first end 104, and the second end 106. The control end 102 is used for receiving the driving signal DRV1, the first end is used for inputting the input voltage Vin, and the second end 106 is coupled to the resistor R. The resistor R has a first end 222 and a second end 224. The first end 222 is coupled to the second end 106 of the driving transistor Q1, and the second end 224 is used for outputting the output voltage Vout. The resistor R is used for measuring the current I1 flowing into the driving transistor Q1. The capacitor C1 is coupled to the input voltage Vin and to the first end 104 of the first end 104 of the driving transistor Q1 for filtering noise from the input voltage Vin. The first resistor R1 has the first end 312 and the second end 314. The first end 312 is coupled to the second end 224 of the resistor R, and the second end 314 is used for outputting the feedback FB1. The second resistor R2 has the first end 322 and the second end 324. The first end 322 is coupled to the second end 314 of the first transistor R1 in series, and the second end 324 is coupled to ground.
The magnitude of the feedback signal FB1 is decided by the ratio of the first resistor R1 to the second resistor R2. The output capacitor Cout is coupled to the output voltage Vout as a loading of the low dropout regulator 22. The controller 24 includes an amplifier 25. The amplifier 25 has a first input end 252, a second input end 254, and an output end 256. The first input end 252 is used for receiving the reference voltage Vref, the second input end 254 is coupled to the second end 314 of the first resistor R1 and to the second end 324 of the second resistor R2 for receiving the feedback signal FB1, and the output end 256 is coupled to the control end 102 of the driving transistor Q1 for outputting the driving signal DRV1 to the driving transistor Q1. The driving transistor Q1 is turned off to protect the driving transistor Q1 when the current I1 measured by the resistor R is too large. The driving transistor Q1 is a metal-oxide semiconductor transistor (MOS).
Typical low dropout regulated circuits presently will not only waste energy but also cause chipsets have a temperature that influences system stability due to large power consumption when working in conditions of a heavy load or a larger current. Moreover, even the driving transistor Q1 is burned out if the low dropout regulated circuits is under a heavy load for a long time. Although the low dropout regulated circuit 20 is capable of detecting the current I1 flowing into the driving transistor Q1 to further provide current protections to the low dropout regulated circuit 20, a resistor R is needed, raising costs and will consume power by itself. The driving transistor Q1 is installed inside the controller 24 and is restricted to a fixed transistor.